Adds ToggleIconButton.
Import button is always shown on screen. Also widgets use the new icons. The correct frame is selected when pausing.
New icons used. Small bugfix while trying to center at a specified index after undoing an import action.
Added new actions with their tests.
Some changes in EditableLabel
Now the labels are represented by EditableLabel in editor.
Now can add text with editor
Merge pull request #693 from gorco/AddText

Added text tool functionality
Merge pull request #694 from RotaruDan/AnimationEditor

Animation editor improvements.